This invention relates to acoustic levitation wherein the force of sound waves are used to suspend, position or manipulate an object such as a solid or liquid.
As described in U.S. Pat. No. 4,284,403, the potential practical applications for acoustic levitation are numerous and varied. Many potential applications exist whenever there is a need to hold, move, store, position, or process an object without contact with any surface, particularly if such contact would damage or contaminate the object or otherwise interfere with some desired property or state of the object. For example, an object which is melted by conventional means at high temperatures will be contaminated by the container, and acoustic levitation offers the possibility of containerless melting as well as other containerless or non-contact processing involving, for example, chemical reaction, alteration of physical shape, agitating, coating, combining, conveying, and the like.
Acoustic levitation also lends itself to manufacturing processes in outer space by preventing drift of materials being processed in zero gravity. Experiments are being conducted to enable processing of acoustically positioned objects in future space stations.
Prior art levitation devices have developed along two separate lines. In one type of device, one or more sound sources are connected to a chamber in which a reflective wall opposes the sound source. The wall is positioned at n(x/2) from the sound source, wherein x is the wavelength of the sound, and n is a whole number. This causes a standing wave pattern to be produced in which objects may be positioned in the pressure nodes of the waves. Acoustic levitation devices which use resonant cavities are shown, for example, in the following U.S. Pat. Nos. 3,882,732; 4,052,181; 4,420,977; 4,393,706; 4,393,708; 4,463,606; and 4,475,921.
There are serious drawbacks in the use of a resonant cavity as described above. The cavity must be contained within an enclosure in which the geometry is critical. In addition, the cavity must be carefully tuned, and variations of temperature cause loss of essential resonance unlesss the cavity is constantly retuned.
Another type of acoustic levitation device is referred to as a single axis levitator. An improved form of this class of device is shown in the aforesaid U.S. Pat. No. 4,284,403. In such a device, sound waves are reflected from a small reflector to create an energy well, based on localized interference, which is independent of resonance or standing waves. Such a device is not sensitive to temperature changes and does not require an enclosure having reflective surfaces. As a result, levitated objects can be easily moved from one position to another in any direction and without regard to the confines of an enclosure or temperature variations. The only potential drawback with such device is that the energy well that supports the levitated object is located near the small reflector.